The present invention relates to computer color printing systems, and more particularly to an iterative process for determining printer colorant levels using color patches displayed on a computer monitor or the like.
Page layouts to be printed will, in addition to the common components of text and images, often contain graphic elements that are to be printed with a specific color. On large printing presses, these xe2x80x9cspotxe2x80x9d colors are printed using additional individual plates, each using an ink that makes the specific color desired.
On smaller printers, or in proofing, the spot colors must be simulated using a combination of the colorants utilized by the printer. These are usually the CMYK xe2x80x9cprocessxe2x80x9d inks, i.e., cyan, magenta, yellow, and black. While certain standard color tables exist for the simulation of some industry colors using standard ink sets, there is a general problem of finding the correct combination of colorant amounts for a given printer in order to match a particular spot color. There is a further problem of finding the colorant amounts necessary to match other target colors beyond those of spot color inks, such as colors of textiles and other colored objects.
A graphic artist or printer operator currently either accepts an approximate color match, based on simplistic or inappropriate color models for the printer, or uses a time consuming and inefficient trial and error process to find a visual match to a desired spot color. It would be advantageous to provide a method for improving the trial and error process into an efficient, directed search through the color space of a desired printer in order to find the colorant amounts required to simulate a spot color ink or to match a desired target color.
The present invention provides an iterative method for determining printer colorant levels having the aforementioned and other advantages.
In accordance with the present invention, a method is provided for determining colorant levels required by a printer to match a target color. A set of candidate colors is generated on a computer and printed on the printer. One or more further sets of candidate colors are then generated on the computer in response to user input indicative of a correlation between a color in a most recent printed set of candidate colors and the target color. The user then chooses a further set of candidate colors to be printed. The steps of generating and printing further sets of candidate colors are repeated, if necessary, until a selected color in the most recent printed set of candidate colors acceptably matches the target color. Information indicative of the colorant levels required by the printer to print the selected color is recorded (e.g., printed and/or stored in memory) for subsequent use by the printer.
In an illustrated embodiment, the sets of candidate colors comprise a center color spot surrounded by a plurality of similarly colored (i.e., related, but non-identical) color spots. A particular color can be provided for the center color spot in response to user input. In particular, the colored spot from the most recent printed set of candidate colors that a user determines best matches the target color can be provided as the next center spot.
The initial set of candidate colors can be, for example, generated from an initial guess for the target color selected from a palette of colors presented to a user by the computer. In an alternate embodiment, the candidate colors are generated from an instrument reading of the target color. For example, a densitometer can be provided to measure the target color, and the output of the densitometer can be coupled to the computer for reading in the target color readings via, e.g., a serial data port or the like. In yet another embodiment, a user is provided with color spacing and colorant level information pertaining to a previously obtained set of candidate colors, and the user enters this information into the computer for use in generating an initial set of candidate colors when commencing a new target color matching process.
An option can be provided to enable the user to adjust a color spacing between individual colors in the set(s) of candidate colors. The sets of candidate colors can each comprise a plurality of color neighbors related by one or any combination of hue, lightness and saturation, and can be presented to the user on a display (e.g., video monitor) associated with the computer.
In an illustrated embodiment, the computer monitor on which the candidate colors are displayed uses an RGB color space, whereas the colors are printed on the printer using a CMYK color space. Thus, in accordance with the invention, the CMYK color space is mapped to the RGB color space. The RGB colors are then encoded for display on the monitor in accordance with the mapping. The mapping step can include an additional parameter T associated with the RGB colors and indicative of a total ink level of the CMYK colors. The use of the T parameter facilitates a unique mapping from CMYK to RGB.
In a preferred embodiment, a plurality of candidate color sets are shown at one time on the monitor. The different sets of the plurality are related by one of lightness and saturation. A user is permitted to choose between the lightness and saturation relationships. Moreover, the user can iteratively select color patches from successively computed and displayed candidate color sets prior to printing a desired set of candidate colors on the printer.